The size of the power supply in Redundant Array of Independent Disks (RAID) controllers is conventionally limited to reduce costs. This forces the controller to limit the number of drives that can be spun-up simultaneously. Spinning up a disk drive may comprise bringing the disk pack thereof from an initial state in which the constituent platters that support the data-carrying magnetic material are not rotating to a state in which the constituent platters are spinning at the target or rated revolutions per minute or rpm. For current disk drives, such target rate may be, for example, 5400, 7200, 10,000 or 15,000 rpm. The number of disk drives that are spun-up simultaneously is limited in conventional arrays to limit the aggregate current draw from the power supply to within the specified capacity of the power supply to source such current. Indeed, if the current draw becomes too large, the power supply may fail, causing an unintended reset of the entire array.
Delayed “Time to First Data”, or the period of time elapsed from initiating spin-up to the time at which the disk drive reports that it is ready to process data access commands, is a consequence of this limitation. This “Time to First Data” is significantly greater than the time necessary to spin-up the disk packs of the disk drives as the disk drives, after having reached their target spin rate, must energize the Voice Coil Motor (VCM) of the head disk assembly (HDA) to swing the actuator(s) over the disk surfaces, achieve sync with the encoded servo sectors and report drive readiness. This delay is a cumulative effect, in that the greater the number of drives in the array, the longer the array takes to come to ready state in which all constituent drives have reported that they are ready to process data access commands.